Fluidic device for medical diagnostics

ABSTRACT

A fluidic medical diagnostic device permits measurement of analyte concentration or a property of a biological fluid, particularly the coagulation time of blood. The device has at one end a sample port for introducing a sample and at the other end a bladder for drawing the sample to a measurement area. A channel carries the sample from the sample port to the measurement area, and a stop junction, between the measurement area and bladder, halts the sample flow. The desired measurement can be made by placing the device into a meter which measures a physical property of the sample—typically, optical transmittance—after it has interacted with a reagent in the measurement area.

CROSS-REFERENCE TO PRIOR PROVISIONAL APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/093,421, filed Jul. 20, 1998

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a fluidic medical diagnostic device formeasuring the concentration of an analyte in or a property of abiological fluid.

[0004] 2. Description of the Related Art

[0005] A variety of medical diagnostic procedures involve tests onbiological fluids, such as blood, urine, or saliva, and are based on achange in a physical characteristic of such a fluid or an element of thefluid, such as blood serum. The characteristic can be an electrical,magnetic, fluidic, or optical property. When an optical property ismonitored, these procedures may make use of a transparent or translucentdevice to contain the biological fluid and a reagent. A change in lightabsorption of the fluid can be related to an analyte concentration in,or property of, the fluid. Typically, a light source is located adjacentto one surface of the device and a detector is adjacent to the oppositesurface. The detector measures light transmitted through a fluid sample.Alternatively, the light source and detector can be on the same side ofthe device, in which case the detector measures light scattered and/orreflected by the sample. Finally, a reflector may be located at oradjacent to the opposite surface. A device of this latter type, in whichlight is first transmitted through the sample area, then reflectedthrough a second time, is called a “transflectance” device. Referencesto “light” throughout this specification and the appended claims shouldbe understood to include the infrared and ultraviolet spectra, as wellas the visible. References to “absorption” are meant to refer to thereduction in intensity as a light beam passes through a medium; thus, itencompasses both “true” absorption and scattering.

[0006] An example of a transparent test device is described in Wells etal. W094/02850, published on Feb. 3, 1994. Their device comprises asealed housing, which is transparent or translucent, impervious, andrigid or semi-rigid. An assay material is contained within the housing,together with one or more assay reagents at predetermined sites. Thehousing is opened and the sample introduced just before conducting theassay. The combination of assay reagents and analyte in the sampleresults in a change in optical properties, such as color, of selectedreagents at the end of the assay. The results can be read visually orwith an optical instrument.

[0007] U.S. Pat. No. 3,620,676, issued on Nov. 16, 1971 to Davis,discloses a colorimetric indicator for liquids. The indicator includes a“half-bulb cavity”, which is compressible. The bulb is compressed andreleased to form a suction that draws fluid from a source, through ahalf-tubular cavity that has an indicator imprinted on its wall. Theonly controls on fluid flow into the indicator are how much the bulb iscompressed and how long the indicator inlet is immersed in the source,while the bulb is released.

[0008] U.S. Pat. No. 3,640,267, issued on Feb. 8, 1972 to Hurtig et al.,discloses a container for collecting samples of body fluid that includesa chamber that has resilient, collapsible walls. The walls are squeezedbefore the container inlet is placed into the fluid being collected.When released, the walls are restored to their uncollapsed condition,drawing fluid into and through the inlet. As with the Davis device,discussed above, control of fluid flow into the indicator is verylimited.

[0009] U.S. Pat. No. 4,088,448, issued on May 9, 1978 to Lilja et al.,discloses a cuvette, which permits optical analysis of a sample mixedwith a reagent. The reagent is coated on the walls of a cavity which isthen filled with a liquid sample. The sample mixes with the reagent tocause an optically-detectable change.

[0010] A number of patents, discussed below, disclose devices fordiluting and/or analyzing biological fluid samples. These devicesinclude valve-like designs to control the flow of the sample.

[0011] U.S. Pat. No. 4,426,451, issued on Jan. 17, 1984 to Columbus,discloses a multi-zone fluidic device that has pressure-actuatable meansfor controlling the flow of fluid between the zones. His device makesuse of pressure balances on a liquid meniscus at the interface between afirst zone and a second zone that has a different cross section. Whenboth the first and second zones are at atmospheric pressure, surfacetension creates a back pressure that stops the liquid meniscus fromproceeding from the first zone to the second. The configuration of thisinterface or “stop junction” is such that the liquid flows into thesecond zone only upon application of an externally generated pressure tothe liquid in the first zone that is sufficient to push the meniscusinto the second zone.

[0012] U.S. Pat. No. 4,868,129, issued on Sep. 19, 1989 to Gibbons etal., discloses that the back pressure in a stop junction can be overcomeby hydrostatic pressure on the liquid in the first zone, for example byhaving a column of fluid in the first zone.

[0013] U.S. Pat. No. 5,230,866, issued on Jul. 27, 1993 to Shartle etal., discloses a fluidic device with multiple stop junctions in whichthe surface tension-induced back pressure at the stop junction isaugmented, for example, by trapping and compressing gas in the secondzone. The compressed gas can then be vented before applying additionalhydrostatic pressure to the first zone to cause fluid to flow into thesecond zone. By varying the back pressure of multiple stop junctions inparallel, “rupture junctions” can be formed, having lower maximum backpressure.

[0014] U.S. Pat. No. 5,472,603, issued on Dec. 5, 1995 to Schembri (seealso U.S. Pat. No. 5,627,041), discloses using centrifugal force toovercome the back pressure in a stop junction. When flow stops, thefirst zone is at atmospheric pressure plus a centrifugally generatedpressure that is less than the pressure required to overcome the backpressure. The second zone is at atmospheric pressure. To resume flow,additional centrifugal pressure is applied to the first zone, overcomingthe meniscus back pressure. The second zone remains at atmosphericpressure.

[0015] European Patent Application EP 0 803 288, of Naka et al.,published on Oct. 29, 1997, discloses a device and method for analyzinga sample that includes drawing the sample into the device by suction,then reacting the sample with a reagent in an analytical section.Analysis is done by optical or electrochemical means. In alternateembodiments, there are multiple analytical sections and/or a bypasschannel. The flow among these sections is balanced without using stopjunctions.

[0016] U.S. Pat. No. 5,700,695, issued on Dec. 23, 1997 to Yassinzadehet al., discloses an apparatus for collecting and manipulating abiological fluid that uses a “thermal pressure chamber” to provide thedriving force for moving the sample through the apparatus.

[0017] U.S. Pat. No. 5,736,404, issued on Apr. 7, 1998, to Yassinzadehet al., discloses a method for determining the coagulation time of ablood sample that involves causing an end of the sample to oscillatewithin a passageway. The oscillating motion is caused by alternatelyincreasing and decreasing the pressure on the sample.

SUMMARY OF THE INVENTION

[0018] The present invention provides a fluidic diagnostic device formeasuring an analyte concentration or property of a biological fluid.The device comprises

[0019] a first layer and second layer at least one of which has aresilient region over at least part of its area, separated by anintermediate layer, in which cutouts in the intermediate layer form,with the first and second layers,

[0020] a) a sample port for introducing a sample of the biological fluidinto the device;

[0021] b) a first measurement area, in which a physical parameter of thesample is measured and related to the analyte concentration or propertyof the fluid;

[0022] c) a first channel, having a first end and a second end, toprovide a fluidic path from the sample port at the first end through thefirst measurement area;

[0023] d) a first bladder at the second end of the first channel,comprising at least a part of the resilient region in at least the firstor second layer and having a volume that is at least about equal to thecombined volume of the first measurement area and first channel; and

[0024] e) a first stop junction in the first channel between the firstmeasurement area and first bladder that comprises a co-aligned throughhole in at least the first or second layer, the through hole beingoverlaid with a third layer.

[0025] In another embodiment, the device comprises

[0026] a first layer, which has a resilient region over at least a partof its area, and a second layer, separated by an intermediate layer, inwhich recesses in a first surface of the intermediate layer form, withthe first layer,

[0027] a) a sample port for introducing a sample of the biological fluidinto the device;

[0028] b) a measurement area, in which the sample undergoes a change ina physical parameter that is measured and related to the analyteconcentration or property of the fluid;

[0029] c) a channel, having a first end and a second end, to provide afluidic path from the sample port at the first end through themeasurement area; and

[0030] d) a bladder, at the second end of the channel, comprising atleast a part of the resilient region in the first layer and having avolume that is at least about equal to the combined volume of themeasurement area and channel; and

[0031] a stop junction in the channel between the measurement area andbladder that comprises two passages substantially normal to the firstsurface of the intermediate layer, each passage having a first end influid communication with the channel and a second end in fluidcommunication with a recess in a second surface of the intermediatelayer, which recess provides fluid communication between the second endsof the passages.

[0032] The device is particularly well adapted for measuring prothrombintime (PT time), with the biological fluid being whole blood and themeasurement area having a composition that catalyzes the blood clottingcascade.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a plan view of a device of the present invention.

[0034]FIG. 2 is an exploded view of the device of FIG. 1.

[0035]FIG. 3 is a perspective view of the device of FIG. 1.

[0036]FIG. 4 is a schematic of a meter for use with a device of thisinvention.

[0037]FIG. 4A depicts an alternative embodiment of an element of themeter of FIG. 4.

[0038]FIG. 5 is a graph of data that is used to determine PT time.

[0039]FIG. 6 is a plan view of an alternative embodiment of a device ofthis invention.

[0040]FIGS. 6A, 6B, and 6C depict a time sequence during which a sampleis admitted to the device of FIG. 6.

[0041]FIG. 7 is a schematic of a device having multiple measurementareas in parallel, multiple stop junctions in parallel, and a singlebladder.

[0042]FIG. 8 is a schematic of a device having multiple measurementareas in series, with a single stop junction, a single bladder, and afilter over the sample port.

[0043]FIG. 9 is a schematic of a device having multiple measurementareas and multiple stop junctions arranged in an alternating series, aswell as multiple bladders.

[0044]FIG. 10 is a schematic of a device that includes multiplemeasurement areas in parallel, a single bladder, and a single bypasschannel.

[0045]FIG. 11 is a schematic of a device having multiple measurementareas in series, multiple stop junctions in series, multiple bladders inseries, and multiple bypass channels.

[0046]FIG. 12 is an exploded view of an injection-molded device of thisinvention.

[0047]FIG. 13 is a perspective view of the device of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

[0048] This invention relates to a fluidic device for analyzingbiological fluid. The device is of the type that relates a physicalparameter of the fluid, or an element of the fluid, to an analyteconcentration in the fluid or to a property of the fluid. Although avariety of physical parameters e.g., electrical, magnetic, fluidic, oroptical—can form the basis for the measurement, a change in opticalparameters is a preferred basis, and the details that follow refer to anoptical device. The device includes a sample application area; abladder, to create a suction force to draw the sample into the device; ameasurement area, in which the sample may undergo a change in an opticalparameter, such as light scattering; and a stop junction to preciselystop flow after filling the measurement area.

[0049] Preferably, the device is substantially transparent over themeasurement area, so that the area can be illuminated by a light sourceon one side and the transmitted light measured on the opposite side. Themeasurement on the sample may be of a parameter that is not changing,but typically the sample undergoes a change in the measurement area, andthe change in transmitted light is a measure of the analyte or fluidproperty of interest. Alternatively, light that is scattered from afluid sample or light that passes through the sample and is reflectedback through a second time (by a reflector on that opposite side) can bedetected by a detector on the same side as the light source.

[0050] This type of device is suitable for a variety of analytical testsof biological fluids, such as determining biochemical or hematologicalcharacteristics, or measuring the concentration in such fluids ofproteins, hormones, carbohydrates, lipids, drugs, toxins, gases,electrolytes, etc. The procedures for performing these tests have beendescribed in the literature. Among the tests, and where they aredescribed, are the following:

[0051] (1) Chromogenic Factor XIIa Assay (and other clotting factors aswell): Rand, M. D. et al., Blood, 88, 3432 (1996).

[0052] (2) Factor X Assay: Bick, R. L. Disorders of Thrombosis andHemostasis: Clinical and Laboratory Practice. Chicago, ASCP Press, 1992.

[0053] (3) DRVVT (Dilute Russells Viper Venom Test): Exner, T. et al.,Blood Coag. Fibrinol., 1, 259 (1990).

[0054] (4) Immunonephelometric and Immunoturbidimetric Assays forProteins: Whicher, J. T., CRC Crit. Rev. Clin Lab Sci. 18:213 (1983).

[0055] (5) TPA Assay: Mann, K. G., et al., Blood, 76, 755, (1990).; andHartshorn, J. N. et al., Blood, 78, 833 (1991).

[0056] (6) APTT (Activated Partial Thromboplastin Time Assay): Proctor,R. R. and Rapaport, S. I. Amer. J. Clin. Path, 36, 212 (1961); Brandt,J. T. and Triplett, D. A. Amer. J. Clin. Path., 76, 530 (1981); andKelsey, P. R. Thromb. Haemost. 52, 172 (1984).

[0057] (7) HbA1c Assay (Glycosylated Hemoglobin Assay): Nicol, D. J. etal., Clin. Chem. 29, 1694 (1983).

[0058] (8) Total Hemoglobin: Schneck et al., Clinical Chem., 32/33, 526(1986); and U.S. Pat. No. 4,088,448.

[0059] (9) Factor Xa: Vinazzer, H., Proc. Symp. Dtsch. Ges. Klin. Chem.,203 (1977), ed. By Witt, I

[0060] (10) Colorimetric Assay for Nitric Oxide: Schmidt, H. H., et al.,Biochemica, 2, 22 (1995).

[0061] The present device is particularly well suited for measuringblood-clotting time—“prothrombin time” or “PT time”—and detailsregarding such a device appear below. The modifications needed to adaptthe device for applications such as those listed above require no morethan routine experimentation.

[0062]FIG. 1 is a plan view of a device 10 of the present invention.FIG. 2 is an exploded view and FIG. 3 a perspective view of the device.Sample is applied to sample port 12 after bladder 14 has beencompressed. Clearly, the region of layer 26 and/or layer 28 that adjoinsthe cutout for bladder 14 must be resilient, to permit bladder 14 to becompressed. Polyester of about 0.1 mm thickness has suitable resilienceand springiness. Preferably, top layer 26 has a thickness of about 0.125mm, bottom layer 28 about 0.100 mm. When the bladder is released,suction draws sample through channel 16 to measurement area 18, whichpreferably contains a reagent 20. In order to ensure that measurementarea 18 can be filled with sample, the volume of bladder 14 ispreferably at least about equal to the combined volume of channel 16 andmeasurement area 18. If measurement area 18 is to be illuminated frombelow, layer 28 must be transparent where it adjoins measurement area18. For a PT test, reagent 20 contains thromboplastin that is free ofbulking reagents normally found in lyophilized reagents.

[0063] As shown in FIGS. 1, 2, and 3, stop junction 22 adjoins bladder14 and measurement area 18; however, a continuation of channel 16 may beon either or both sides of stop junction 22, separating the stopjunction from measurement area 18 and/or bladder 14. When the samplereaches stop junction 22, sample flow stops. For PT measurements, it isimportant to stop the flow of sample as it reaches that point to permitreproducible “rouleaux formation”—the stacking of red blood cells—whichis an important step in monitoring blood clotting using the presentinvention. The principle of operation of stop junctions is described inU.S. Pat. No. 5,230,866, incorporated herein by reference.

[0064] As shown in FIG. 2, all the above elements are formed by cutoutsin intermediate layer 24, sandwiched between top layer 26 and bottomlayer 28. Preferably, layer 24 is double-sided adhesive tape. Stopjunction 22 is formed by an additional cutout in layer 26 and/or 28,aligned with the cutout in layer 24 and sealed with sealing layer 30and/or 32. Preferably, as shown, the stop junction comprises cutouts inboth layers 26 and 28, with sealing layers 30 and 32. Each cutout forstop junction 22 is at least as wide as channel 16. Also shown in FIG. 2is an optional filter 12A to cover sample port 12. The filter mayseparate out red blood cells from a whole blood sample and/or maycontain a reagent to interact with the blood to provide additionalinformation. A suitable filter comprises an anisotropic membrane,preferably a polysulfone membrane of the type available from SpectralDiagnostics, Inc., Toronto, Canada. Optional reflector 18A may be on, oradjacent to, a surface of layer 26 and positioned over measurement area18. If the reflector is present, the device becomes a transflectancedevice.

[0065] The method of using the strip of FIGS. 1, 2, and 3 can beunderstood with reference to a schematic of the elements of a metershown in FIG. 4, which contemplates an automated meter. Alternatively,manual operation is also possible. (In that case, bladder 14 is manuallydepressed before sample is applied to sample port 12, then released.)The first step the user performs is to turn on the meter, therebyenergizing strip detector 40, sample detector 42, measurement system 44,and optional heater 46. The second step is-to insert the strip.Preferably, the strip is not transparent over at least a part of itsarea, so that an inserted strip will block the illumination by LED 40 aof detector 40 b. (More preferably, the intermediate layer is formed ofa non-transparent material, so that background light does not entermeasurement system 44.) Detector 40 b thereby senses that a strip hasbeen inserted and triggers bladder actuator 48 to compress bladder 14. Ameter display 50 then directs the user to apply a sample to sample port12 as the third and last step the user must perform to initiate themeasurement sequence. The empty sample port is reflective. When a sampleis introduced into the sample port, it absorbs light from LED 42 a andthereby reduces-the light that is reflected to detector 42 b. Thatreduction in light, in turn, signals actuator 48 to release bladder 14.The resultant suction in channel 16 draws sample through measurementarea 18 to stop junction 22. Light from LED 44 a passes throughmeasurement area 18, and detector 44 b monitors the light transmittedthrough the sample as it is clotting. When there are multiplemeasurement areas, measurement system 44 includes an LED/detector pair(like 44 a and 44 b) for each measurement area. Analysis of thetransmitted light as a function of time (as described below) permits acalculation of the PT time, which is displayed on the meter display 50.Preferably, sample temperature is maintained at about 37° C. by heater46.

[0066] As described above, the detector senses a sample in sample port12, simply by detecting a reduction in (specular) reflection of a lightsignal that is emitted by 42 a and detected by 42 b. However, thatsimple system cannot easily distinguish between a whole blood sample andsome other liquid (e.g., blood serum) placed in the sample port in erroror, even, an object (e.g., a finger) that can approach sample port 12and cause the system to erroneously conclude that a proper sample hasbeen applied. To avoid this type of error, another embodiment measuresdiffuse reflection from the sample port. This embodiment appears in FIG.4A, which shows detector 42 b positioned normal to the plane of strip10. With the arrangement shown in FIG. 4A, if a whole blood sample hasbeen applied to sample port 12, the signal detected by 42 b increasesabruptly, because of scattering in the blood sample, then decreases,because of rouleaux formation (discussed below). The detector system 42is thus programmed to require that type of signal before causingactuator 48 to release bladder 14. The delay of several seconds inreleasing bladder 14 does not substantially affect the readingsdescribed below

[0067]FIG. 5 depicts a typical “clot signature” curve in which thecurrent from detector 44 b is plotted as a function of time. Blood isfirst detected in the measurement area by 44 b at time 1. In the timeinterval A, between points 1 and 2, the blood fills the measurementarea. The reduction in current during that time interval is due to lightscattered by red cells and is thus an approximate measure of thehematocrit. At point 2, sample has filled the measurement area and is atrest, its movement having been stopped by the stop junction. The redcells begin to stack up like coins (rouleaux formation). The rouleauxeffect allows increasing light transmission through the sample (and lessscattering) in the time interval between points 2 and 3. At point 3,clot formation ends rouleaux formation and transmission through thesample reaches a maximum. The PT time can be calculated from theinterval B between points 1 and 3 or between 2 and 3. Thereafter, bloodchanges state from liquid to a semi-solid gel, with a correspondingreduction in light transmission. The reduction in current C between themaximum 3 and endpoint 4 correlates with fibrinogen in the sample.

[0068] The device pictured in FIG. 2 and described above is preferablyformed by laminating thermoplastic-sheets 26 and 28 to a thermoplasticintermediate layer 24 that has adhesive on both of its surfaces. Thecutouts that form the elements shown in FIG. 1 may be formed, forexample, by laser- or die-cutting of layers 24, 26, and 28.Alternatively, the device can be formed of molded plastic. Preferably,the surface of sheet 28 is hydrophilic. (Film 9962, available from 3M,St. Paul, Minn.) However, the surfaces do not need to be hydrophilic,because the sample fluid will fill the device without capillary forces.Thus, sheets 26 and 28 may be untreated polyester or other thermoplasticsheet, well known in the art. Similarly, since gravity is not involvedin filling, the device can be used in any orientation. Unlike capillaryfill devices that have vent holes through which sample could leak, thepresent device vents through the sample port before sample is applied,which means that the part of the strip that is first inserted into themeter is without an opening, reducing the risk of contamination.

[0069]FIG. 6 is a plan view of another embodiment of the device of thepresent invention, in which the device includes a bypass channel 52 thatconnects channel 16 with bladder 14. The function and operation of thebypass channel can be understood by referring to FIGS. 6A, 6B, and 6Cwhich depict a time sequence during which a sample is drawn into device10 for the measurement.

[0070]FIG. 6A depicts the situation after a user has applied a sample tothe strip, while bladder 14 is compressed. This can be accomplished byapplying one or more drops of blood.

[0071]FIG. 6B depicts the situation after the bladder is decompressed.The resulting reduced pressure in the inlet channel 16 draws the sampleinitially into the measurement area 18. When the sample reaches stopjunction 22, the sample encounters a back pressure that causes it tostop and causes additional sample to be drawn into the bypass channel.

[0072]FIG. 6C depicts the situation when a reading is taken. Sample isisolated and at rest in measurement area 18. Excess sample and/or airhas been drawn into bypass channel 52.

[0073] The bypass channel of FIG. 6 provides an important improvementover the operation of the “basic” strip of FIGS. 1-3. In the basicstrip, stop junction 22 stops the flow of sample after it fillsmeasurement area 18. As was discussed earlier, it is important to stopthe flow in order to facilitate rouleaux formation. As was alsodiscussed earlier, the stop junction accomplishes the flow stoppage as aresult of surface tension acting on the meniscus at the leading edge ofthe fluid at an abrupt change in cross section of the flow channel. Inthe basic strip, the pressure on the bladder side of the stop junctionremains below atmospheric pressure while the pressure on the sample sideremains open to atmosphere. Thus, there is an ambient pressure imbalanceon the two sides. The greater the imbalance, the greater the risk thatthe stop junction will leak and that sample will flow through the stopjunction, interfering with rouleaux formation, and, consequently,providing inaccurate values of PT.

[0074] Bypass channel 52 minimizes that risk. The reduced pressure onthe bladder side of the stop junction draws sample into the bypasschannel (FIGS. 6B, 6C) until the ambient pressure is equalized atatmospheric pressure on both sides of the stop junction. Note that the(reduced) pressure on the bladder side is relatively uncontrolled. Thebypass channel 52, by enabling the pressures on the two sides of thestop junction to equilibrate, permits the use of larger bladders thathave greater suction. Larger bladders, in turn, provide more reliableoperation of the system.

[0075]FIG. 7 depicts an embodiment of the present invention in whichthere are multiple (three are shown) measurement areas “in parallel”.That is to say that the channels 116P, 216P, and 316P fill substantiallysimultaneously (assuming they have the same dimensions). The situationdepicted in FIG. 7, with channels and measurement areas filled withblood, is achieved, as discussed above, by applying sample to sampleport 112 while bladder 114 is compressed, then releasing bladder 114. Asdiscussed above, the first step is to apply sample to sample well 112while bladder 114 is compressed. The second step is to release thebladder. Sample flows to measurement areas 118P, 218P, and 318P, andflow stops when sample reaches stop junctions, 122P, 222P, and 322P,respectively. The optional second and third measurement areas maycontain, for example, reagents that neutralize the presence ofinterferents (such as heparin) in the blood, or that provide a built-incontrol on the PT measurement, or that measure another blood parameter(such as APPT)

[0076]FIG. 8 is a schematic illustration of an embodiment in whichmultiple measurement areas are “in series”, meaning that they fillsequentially. In this embodiment, measurement areas 118S, 218S, and 318Sfill sequentially, through a single channel 116S, until the samplereaches stop junction 122S. A potential drawback of this design is thatsample passing from one measurement area to the next may carry overreagent.

[0077]FIG. 9 is a schematic of another embodiment of a device that isadapted for multiple sequential tests. In that embodiment stop junctions122T, 222T, and 322T permit a user to control the timing of sequentialfilling of measurement areas 118T, 218T, and 318T. In operation,bladders 114, 214, and 314 are all compressed before a blood sample isapplied to sample well 112. Bladder 114 is then released to draw bloodinto measurement area 118T to stop junction 122T. At a selected latertime, bladder 214 is released to permit blood to break through stopjunction 122T and enter measurement area 218T to stop junction 222T.Finally, when the user wishes to use measurement area 318T, bladder 314is decompressed, permitting sample to break through stop function 222Tand flow to stop junction 322T. The device of FIG. 9 must be carefullyformed, since the force drawing sample into the device—caused bydecompressing a bladder—must be balanced against the opposingforce—exerted by a stop junction. If the drawing force is too great, astop junction may prematurely permit 'sample to pass; if it's too small,it will not draw the sample through a stop junction, when that isintended.

[0078]FIG. 10 depicts a preferred embodiment of the present device. Itis a parallel multi-channel device that includes bypass channel 152P.Bypass channel 152P serves a purpose in this device that is analogous tothat served by bypass channel 52 in the device of FIG. 6, which wasdescribed above. Measurement area 118P contains thromboplastin.Preferably, measurement areas 218P and 318P contain controls, morepreferably, the controls described below. Area 218P containsthromboplastin, bovine eluate, and recombinant Factor VIIa. Thecomposition is selected to normalize the clotting time of a blood sampleby counteracting the effect of an anticoagulant, such as warfarin.Measurement area 318P contains thromboplastin and bovine eluate alone,to partially overcome the effect of an anticoagulent. Thus, 3measurements are made on the strip. PT time of the sample, themeasurement of primary interest, is measured on area 118P. However, thatmeasurement is validated only when measurements on areas 218P and 318Pyield results within a predetermined range. If either or both of thesecontrol measurements are outside the range, then a retest is indicated.Extended stop junction 422 stops flow in all three measurement areas.

[0079]FIG. 11 depicts a device that includes bypass channels 152S and252S to permit timed filling of measurement areas 118T and 218T.Operation of the device of FIG. 11 is analogous to that of the device ofFIG. 9, described above, with the following exception. First bypasschannel 152S has a region in which a reagent that causes clotting, suchas thromboplastin, is coated. As a first measurement is made in reagentarea 118T, a clot forms in blood that had been drawn into bypass channel152S. Thus, when the second bladder is decompressed, blood is blockedfrom being drawn through bypass 152S and instead is drawn though stopjunction 122T to measurement area 218T and bypass channel 252S.

[0080] All the previous figures depict the device of this invention as alaminated strip structure; however, the device could also be aninjection-molded structure of the type shown in FIGS. 12 and 13. FIG. 12is an exploded view of an injection-molded device 110, including toplayer 126 and bottom layer 128 sandwiching intermediate layer 124. Theintermediate layer has depressions in its top surface that form sampleport 112, channel 116, measurement area 118, and optional bypass channel152. Stop junction 122 passes through the thickness of intermediatelayer 124. Sample flow stops at the interface between stop junction 122and channel A, which is formed by a depression in the bottom surface.Thus, the sample flows from sample port 112 through channel 116 tomeasurement area 118 into stop junction 122.

[0081] The principle of operation of the injection molded device is thesame as described above. It provides greater flexibility in the designof the stop junction, as well as the other elements of the device,because a wide range of channel cross sections are feasible. The moldedstructure also provides more rigidity, although it is substantially morecostly.

[0082] The following examples demonstrate the present invention in itsvarious embodiments, but are not intended to be in any way limiting.

EXAMPLE 1

[0083] A strip of this invention is made by first passing a double-sidedadhesive tape (RX 675SLT, available from Scapa Tapes, Windsor, Conn.)sandwiched between two release liners into a laminating and rotarydie-cutting converting system. The pattern shown in FIG. 6, with theexception of the stop junction, is cut through the top release liner andtape, but not through the bottom release liner, which is then removed aswaste, along with the cutouts from the tape. Polyester film treated tobe hydrophilic (3M9962, available from 3M, St. Paul, Minn.) is laminatedto the exposed bottom side of the tape. Reagent (thromboplastin,available from Ortho Clinical Diagnostics, Raritan, N.J.) is thenprinted onto the reagent area (18) of the polyester film by bubble jetprinting, using printing heads 51612A, from Hewlett Packard, Corvallis,Oreg. A sample port is cut in untreated polyester film (AR1235,available from Adhesives Research, Glen Rock, Pa.) and then laminated,in register, to the top of the double-sided tape (after removing therelease layer). A die then cuts the stop junction through the threelayers of the sandwich. Finally, strips of single-sided adhesive tape(MSX4841, available from 3M, St. Paul, Minn.) are applied to the outsideof the polyester layers to seal the stop junction.

EXAMPLE 2

[0084] A procedure that is similar to the one described in Example 1 isfollowed to make a strip of the type depicted in FIG. 10. Reagent thatis bubble-jet printed onto areas 118P, 218P, and 318P is, respectively,thromboplastin; thromboplastin, bovine eluate, and recombinant FactorVIIa; and thromboplastin and bovine eluate alone. The bovine eluate(plasma barium citrate bovine eluate) is available from HaemotologicTechnologies, Burlington, Vt.; and recombinant Factor VIIa from AmericanDiagnostica, Greenwich, Conn.

[0085] Measurements made on a whole blood sample using the strip of thisExample yield a curve of the type shown in FIG. 5 for each of themeasurement areas. The data from the curves for the controls(measurement areas 218P and 318P) are used to qualify the data from thecurve for measurement area 118P. As a result, the PT time can bedetermined more reliably than can be done with a strip having a singlemeasurement area.

EXAMPLE 3

[0086] The device of FIGS. 12 and 13 is formed by sandwiching middlelayer 124 between top layer 126 and bottom layer 128. The middle andbottom layers are injection molded polycarbonate (Lexan*121) and havethicknesses of 6.3 mm and 1.5 mm, respectively. Top layer 126 is made bydie cutting 0.18 mm Lexan* 8010 sheet. The elements are ultrasonicallywelded after the reagent of Example 1 is applied to reagent area 118.The Lexan* material is available from General Electric, Pittsfield,Mass.

[0087] The invention having been fully described, it will be apparent toone of ordinary skill in the art that many modifications and changes maybe made to it without departing from the spirit and scope of the presentinvention.

We claim:
 1. A fluidic diagnostic device for measuring an analyteconcentration or property of a biological fluid, comprising a firstlayer and second layer, at least one of which has a resilient regionover at least a part of its area, separated by an intermediate layer, inwhich cutouts in the intermediate layer form, with the first and secondlayers, a) a sample port for introducing a sample of the biologicalfluid into the device; b) a first measurement area, in which a physicalparameter of the sample is measured and related to the analyteconcentration or property of the fluid; c) a first channel, having afirst end and a second end, to provide a fluidic path from the sampleport at the first end through the first measurement area; d) a firstbladder, at the second end of the first channel comprising at least apart of the resilient region in at least the first or second layer andhaving a volume that is at least about equal to the combined volume ofthe first measurement area and first channel; and e) a first stopjunction in the first channel between the first measurement area andfirst bladder that comprises a co-aligned through hole in the first orsecond layer, the through hole overlaid with a third layer.
 2. Thedevice of claim 1 in which the sample port comprises co-aligned throughholes in the first and intermediate layers.
 3. The device of claim 1 inwhich the first stop junction further comprises a second through holealigned with the first through hole, the second through hole beingoverlaid with a fourth layer.
 4. The device of claim 1, furthercomprising a bypass channel, to provide an additional path from thefirst channel to the bladder, without traversing the first measurementarea and first stop junction.
 5. The device of claim 1 in which at leastthe first or second layer is substantially transparent adjoining thefirst measurement area, and the physical parameter that is measured isoptical transmission.
 6. The device of claim 5 further comprising areflective surface adjoining the first measurement area.
 7. The deviceof claim 1 in which the physical parameter of the sample undergoes achange in the measurement area.
 8. The device of claim 7 in which thefirst measurement area contains a composition that facilitates bloodclotting, the biological fluid is whole blood, and the property beingmeasured is prothrombin time.
 9. The device of claim 8 in which thecomposition comprises thromboplastin.
 10. The device of claim 1 furthercomprising a filter adjoining the sample port for filtering thebiological fluid being introduced into the sample port.
 11. The deviceof claim 10 in which the filter comprises an anisotropic membrane. 12.The device of claim 11 in which the filter material is polysulfone. 13.The device of claim 1 further comprising at least one additionalmeasurement area between the first measurement area and the stopjunction.
 14. The device of claim 1 further comprising at least onealternate fluidic path from the first channel to the bladder, each suchalternate path including a corresponding measurement area and stopjunction.
 15. The device of claim 4 in which the first measurement areacontains a composition that facilitates blood. clotting, the biologicalfluid is whole blood, and the property being measured is prothrombintime.
 16. The device of claim 15 further comprising at least onealternate fluidic path from the first channel to the bladder, each suchalternate path including a corresponding measurement area and stopjunction.
 17. The device of claim 16 in which a first alternate path isto a measurement area that overcomes the effect of an anticoagulant anda second alternate path is to a measurement area that partiallyovercomes the effect of an anticoagulant.
 18. The device of claim 17 inwhich the measurement area in the first alternate path comprisesthromboplastin, bovine eluate, and recombinant Factor VIIa and themeasurement area in the second alternate path comprises thromboplastinand bovine eluate.
 19. The device of claim 13 further comprising atleast one set of channel, measurement area, and stop junction betweenthe first stop junction and first bladder and, adjoining the firstbladder, an additional bladder for each such set.
 20. The device ofclaim 19 further comprising a bypass channel from the first channel tothe first bladder and an additional bypass channel from the channel ofeach. additional set to the corresponding additional bladder.
 21. Afluidic diagnostic device for measuring an analyte concentration orproperty of a biological fluid, comprising a first layer, which has aresilient region over at least a part of its area, and a second layer,separated by an intermediate layer, in which recesses in a first surfaceof the intermediate layer form, with the first layer, a) a sample portfor introducing a sample of the biological fluid into the device; b) ameasurement area, in which the sample undergoes a change in a physicalproperty that is measured and related to the analyte concentration orproperty of the fluid; c) a channel, having a first end and a secondend, to provide a fluidic path from the sample port at the first endthrough the measurement area; and d) a bladder, at the second end of thechannel, comprising the resilient region in the first layer and having avolume that is at least about equal to the combined volume of themeasurement area and channel; and a stop junction in the channel betweenthe measurement area and bladder that comprises two passagessubstantially normal to the first surface of the intermediate layer,each passage having a first end in fluid communication with the channeland a second end in fluid communication with a recess in a secondsurface of the intermediate layer, which recess provides fluidcommunication between the second ends of the passages.